Identification and characteristics analysis of toll-like receptors family genes in yak

Toll-like receptors (TLRs) are innate pattern recognition receptors that play an important role in host resistance to pathogenic microbes. In this study, we cloned the coding region of the yak TLR family (1–10) genes and used bioinformatics to analyze gene characteristics. Real-time fluorescence quantitative polymerase chain reaction was used to detect TLR expression levels in different tissues. Yak TLR genes exhibited high homologies with other species. At the nucleotide level, yak shared more than 96 % homology with cattle and sheep and 75–87 % homology with human and mouse. At the amino acid level, yak shared 90–99 % homology with cattle and sheep and 64–86 % homology with human and mouse. Yak showed close evolutionary relationship with cattle and sheep, which formed a branch of mammals together with TLRs from human, horse, and mouse, among others, and formed a branch with a longer genetic distance with chicken. TLR1, 2, 6, and 10 and TLR7, 8, and 9 were clustered in 2 individual branches, respectively. Fluorescent quantitation results showed that TLRs were expressed in all yak tissues, but different members showed different expression patterns. TLR2, 4, and 6 showed the highest expression in the spleen, followed by ovary, small intestine, kidney, and liver. TLR1, 5, 7, 8, 9, and 10 were most highly expressed in the kidney and showed higher expression in the liver, kidney, spleen, and other tissues. Our results will be useful for studies on immune molecular mechanisms and disease resistance breeding of yak and other plateau animals.